Asphaltic molding compositions and molded articles containing wood fiber



tent:

2,806,825 Patented Sept. 17, 1957 ASPHALTEC MOLDENG COWGSITIONS ANDMOLDED ARTICLES CGNTA INING WU'IED FIBER No Drawing. Application June26, 1952, Serial No. 2%,820

Claims. (Cl. 269-?) The current art of manufacture of bituminous moldedarticles of acid-resistant character, e. g. storage battery cases,utilizes asphalt as a binder, an acid-resistant mineral matter such astalc as a hardness-imparting filler, and cotton linters as a fibroustoughening agent. By proper choice, proportioning and mixing of suchingredients storage battery cases can be made which meet the many andrigid physical tests now established for such articles, and which areacid-resistant in the sense that they stand up in the continued presenceof acid solutions such as the sulfuric acid electrolyte of lead-acidaccumulators. It was pointed out in the Lukens Patent 1,752,917 (nowexpired) that acid resistance could be attained in such molded articlesif the quantity of organic fiber was kept below about by weight of thecomposition.

Molded articles of this class are subject to the peculiar phenomenon ofacid penetration. While the composition is acid resistant in the senseabove, any aqueous liquid including the storage battery electrolyte hasa tendency gradually to penetrate into the walls of the molded article.The rate of penetration may, under certain circumstances, be so slow asnot to interfere with the useful life of the article; but if, say in apartition between cells, the electrolyte acting from both sides shouldpenetrate entirely through the wall section, an electrical path Will beestablished between the adjacent cells with consequent impairment of theefi'iciency of the storage battery. The precise mechanism of acidpenetration is not known, since it does not appear to be explainable byreference alone to the wicking action of the fibers which, in properlymolded structure, are not normally exposed at molded surfaces. It iscustomary in the great bulk of storage batteries made today to confinethe total quantity of organic fiber present to about 11% by weight ofthe composition.

In Patent 2,501,995, Edward R. Dillehay taught a way of decreasing acidpenetration by incorporating into the composition a small quantity of asynthetic resin capable of setting up to an acid-resistant state whencatalyzed by the presence of acid. When the resin so incorporatedpersists in the molded article in an incompletely polymerized condition,the presence of acid against the walls results n the formation in situof some sort of acid barrier. The walls, while retaining theirpenetrability by other aqueous liquids, show a greatly retardedpenetrability by acids and acid solutions. Some penetrability by acidremains, however, in compositions in which the resin content is small;and it is a general rule that, with or without the resin, penetrationwill increase with increases in the fibrous content, though at differentrates.

Cotton linters has hitherto been generally regarded as the onlycommercially important fibrous reinforcement for bituminous storagecases and similar uses. Many attempts have been made to use otherfibers, animal, vegetable and mineral, but these have encountereddifficulties, either in processing, in various aspects of economy, or inthe qualities of the finished product.

Cotton linters has hitherto been an economically available fibrousreinforcement having a fairly uniform and advantageous fiber length inview of the nature of the fibers themselves. Nevertheless, difficultiesare encountered iu the use of linters. The fiber is not always ofuniform quality. It is frequently contaminated with undesirable foreignmaterials, and is often matted or otherwise in poor condition so thatpretreatments are advisable. Such pretreatments require investment inmachinery, and involve time delays. Moreover, cotton linters iscurrently becoming less readily available, and hence more costly to use.

One of the objects of the invention is the provision of new moldedarticles and modes of making them which eliminate cotton in whole or inpart as a fibrous reinforcement.

Another object of the invention is the provision of molded articles ofthe classes to which this specification pertains, which articles haveimproved physical properties and lessened acid penetration, and theprovision of modes of making them.

Yet another object of the invention is the attainment of economic andprocessing advantages in the production of such molded articles.

These and other objects of the invention, which will be set forthhereinafter or will be apparent to one skilled in the art upon readingthese specifications, I accomplish by those procedures and in thosecompositions and molded articles of which I shall now describe certainexemplary embodiments.

I have found that a certain class of fibers derived from wood possessessome new and unexpected properties when employed in compositions of theclasses to which this invention relates. It is not practicable, however,merely to substitute these fibers for cotton in compositions otherwiseidentical. Rather, the successful use of these fibers depends upon theutilization of their unexpected properties in ways which willhereinafter be fully explained.

First, by Way of definition of the class of fiber to which I refer, thecurrent term in the art is exploded wood fiber. Such fiber is preparedby placing green wood chips or shreds in an atmosphere of steam underpressure in a suitable vessel, and then rapidly releasing the pressure,whereupon the substantially instantaneous evaporation of water from thechips or shreds causes them to explode and fiberize. Such a procedure iswell recognized in the art, and fibers produced in this fashion arewidely used in the manufacture of insulation, Wallboard, hard board andthe like. Neither the wood nor the resultant fiber are ordinarilysubjected to any chemical treatment, and none is necessary for mypurposes. While some chemical treatment may be practiced withoutdeparting from the spirit of this invention, I do not contemplate suchdigestion or other chemical treatment as would essentially change thenature of the fibre, nor destroy the general and recognized character ofthe fibrous product as exploded wood fibre as understood in the art, andas can be seen under the microscope.

Not all exploded wood fiber is identical, nor do all available explodedwood fibers are for the most part alder, 1

cottonwood, Douglas fir, and hemlock.

Hereinafter for convenience I shall use the term exploded wood for thefiber. Also, although the term filler is frequently used to cover all ofthe ingredients storage battery cases'current in the art is thefollowing:

. Percent Asphalt 46.2 Talc 40.0 Cotton linters 11.0 Acid-catalyzable.resin 2.8

the; percentages being by weight.

Where: the asphalt is properly chosen (andin this connection referenceis made to the Dillehay Patent 2,501,- 995 )-and the ingredient properlymixed and molded, successful storage battery casesmay be made meetingall of the; physical'and electrical tests current in the art.

The substitution of an equivalent weight of exploded wood for the cottonlinters in the above formula will result in an immediate and seriousloss in impact resistance, in a conventional test performed bysubjecting the wall of a molded article to repeated blows from astandard falling or swinging object. Also, there will be losses intensile strength and elongation under standard tests. Containers soproduced are not of commercial interest by todays standards.

I have ascertained, however, that bituminous compositions made on theabove formula with exploded'wood had exceptionally low acid absorpt ionvalues as compared with the composition containing cotton. Acidabsorption tests are conducted by immersing samples cut from the wallsof molded containers in storage battery electrolyte under standardizedconditions for varying lengths of time and ascertaining the actualabsorption of the electrolyte by the samples on a weight percentagebasis. The tests give an indication of penetration. The use of anincompletely polymerized, acid-catalyzable. resin in building up an acidbarrier and in retarding the rate of acid penetration has been notedhereinabove. The specific effect will vary with the total quantity ofresin in the article, which in turn involves economic considerations;but with minute quantities of resin as in the above formula, the effectismost pronounced. on molded surfaces. Where the samples have cutsurfaces of large area, as in the described test,

where the contained fibers are exposed, cotton compositions. show agreatly retarded acid absorptionbut nevertheless an absorption which isprogressive with elapsed time, with small amounts of resin. For example,samples from a. cotton composition tested for 106 days showed anabsorption of about 3% at the end of that time, the absorption curveindicating that the absorption was still increasing.

By contrast, samples from a composition in which e ploded wood wassubstituted in equal quantity for the cotton in the above formula (theresin content remaining the same) showed an absorption of about .6% atthe end of about 28 days, after which the absorption did notsignificantly increase to the end of the l06 '-day span of the testperiod. In other words, the curve representing absorption values asagainst time became asymptotic toa maximum absorption value irrespectiveof the fact that the samples also had the usual cut-surfaces. At a laterperiodit was ascertained that this was a characteristic behavior ofasphalt-resin-exploded woodcompositions within rather wide limits offormula. Compositions containing different quantities of exploded woodshow different maximum absorption values; but the various curves tend tobecome asymptotic to these values. Thusexplodedwood appears to coactwith resin-blended 4 bitumen in a way which is not identical with thecoaction of cotton.

As a consequence, work was started in an endeavor to improve thephysical properties of asphaltic compositions containing exploded woodwhile maintaining the acid properties equal to or superior to those ofcotton compositions. It was found that this was possible, because withan increase in the content of exploded wood, the impact and tensilevalues rapidly improved while the acid absorption, and in particular thelong-time acid absorption, did not greatly increase. By way of a singleexample, acid absorption samples of a composition containing about 14 /2of exploded wood by weight showed an acid absorption of about 1.4% andwere not increasing at the end of the 106-day test period, whereas asbefore mentioned, a composition containing 11% of cotton fibers hadreached an acid absorption value of about 3% in the same length of timeand was still increasing in acid absorption. An increase in thepercentage of fibrous reinforcement in a bituminous composition could beexpected to raise the impact value; but so far as I know, the combinedproperties of good impact and resistance to acid absorption are peculiarto exploded wood fibers, and do not hold true for any other fibers oforganic origin of which I am aware- Thus, with papermakers fiber, if thefiber ratio is raised to improve impact, this must'be done at thesacrifice of acid resistance which already is no better than that ofcotton on an equal weight basis, and at the same low resin content ofthe composition.

'In increasing the amount of fibrous reinforcement in v a givencomposition, this should not be done haphazardly, or at the expense ofthe binder. As fiber ratios are increased, th eamount of mineral fillershould be reduced. This can be done and is frequently done on thebasis'of experience; but it is entirely possible otherwise to arrive atproportions which will give the maximum strength and impact resistancefrom the materials involved. By way of example, if some particularfibrous material is mixed with an asphaltic binder in varyingproportions, it will be found that some particular proportion gives thegreatest strength and impact resistance. The exact proportion will varysomewhat with different binders, and more importantly with differentfibrous materials. With any given ingredients, the composition of utmoststrength and impact resistance may be called composition A. Similarly, a

Using an exemplary binder having a melting point of 290 to 300 F. andapenetration between 16 and 22, in.

accordance with A.S.T.M. standards, at a temperature of 150 F., under aload of gms. applied-for a time of 5 seconds, it was found (a) that forevery part of exploded wood fibre from 2 to 2.2.parts by weight of thebinder was required to give maximum tensile strength and impactresistance, and (b) for every part of talc there was required about 0.49part of the binder by weight to give maximum physical properties.

Assume a composition were desired containing 11% fibre. The fibre woulditself require 22% of the binder. Adding, say, 3% for the resin, we nowhave a total of 36% or 36 parts by weight. The diiference between thisand 100% (namely 64% or 64 parts) is the asphalttalc mixture making upthe balance of the composition, the talc-asphalt ratio being 1:0.49' asset forth above. This does not mean that actual binder fi'bre andbinderfiller mixtures must be; made and blended. together, al-

mixture above figures at about 41.5 parts talcand 22.5

asse ses I II 111 Percent Percent Percent Binder (asphalt and resin).45. 5 51.0 58.0 Exploded W'ood Fibre 9.0 15.0 22.0 Talc 45. 5 34. 20. 0

As had already been indicated, a composition containing only 9% ofexploded wood fiber as its sole fibrous ingredient will be deficient inimpact value, although showing a very low absorptivity for acid. Usingconventional asphaltic binders, such as the one noted above, it isusually necessary to increase the quantity of exploded wood fiber toabout 13% to equal the impact value obtainable with about 11% of a goodgrade of cotton linters. At a content of 13% exploded wood fiber,however, the acid penetration of the composition is still superior tothat of the cotton composition; and it has been my experience that in acomposition containing 2.8% resin, the quantity of exploded wood fibercan be increased to about 16% while retaining an absorptivity for acidequal or superior to that of an 11% cotton composition. Such anincrease, of course, gives measurably improved impact values.

conservatively speaking 14% of exploded wood will give at most as low anacid absorption value as 11% of cotton, and 11% of exploded wood willgive at most as low an acid absorption value as 8% to 9% of cotton, withor without resin. Without attempting to set an upper limit on acidabsorption, it may be pointed out that acid absorption can be diminishedby increasing the resin content of the composition, taking into accounteconomic considerations. The acid absorption of a composition containingas much as 25 exploded Wood fiber and resin is not significantly greaterthan the absorption of a composition containing 13% of exploded woodfibre and about 2.8% or 3% resin.

Generally, I teach compositions containing substantially 13% to 25%exploded wood fibre (where this is the sole fibrous ingredient), andsubstantially 40 to 13% filler (such as talc or equivalent), the balancebeing bituminous binder plus small amounts of resin, and/ or son emodification agent such as rubber hydrocarbon.

It was also observed that the penetration of plastic bituminouscompositions containing exploded wood fibers, i. e. the stiffness orviscosity of such compositions at given temperatures, as well as thebulge test results on articles molded therefrom, tended to be well belowspecifications and well below the values given by comparable amounts ofcotton linters in similar compositions. Therefore, it was reasoned thata somewhat softer binder could be employed both to improve mixingconditions and to increase the impact resistance without resulting in amolded article having an excessive tendency to bulge under given strainsand temperatures. This is a factor which, so far as i know, is 850unique to exploded wood. It will be understood that bulge resistance isimproved by increasing the amount of fibrous reinforcement in acomposition; but it is characteristic of exploded wood that the bulgeresistances are so high on an equal percentage weight basis that asofter binder may readily be employed to incre se impact resistance asset forth. There is, naturally, a limit to the employment of softerbinder substances, and I do not generally recommend a penetration of thecomposition lower than about 22. Such a penetration may be taken in thesame way penetrations are taken of asphaltic binders alone, inaccordance with the A. S. T. M. standards at a temperature of 150 F.,under a load of 100 gms. applied for a time of 5 seconds.

Other advantages flow from the use of exploded wood in compositions andmolded articles of this class. By way of example, Where the quantity ofexploded wood is greater than the currently used quantities of cottonfiber in comparable articles, the specific gravity of the moldedstructure is less since the increase in fiber is taken at the expense ofa heavier mineral filler. This makes the articles easier to handle, andless expensive to ship and store.

The exploded wood mixes well with the other ingredients of compositionsof this class. The mixing procedures which I employ with exploded woodfibers do not differ from those hitherto used with cotton-containingcompositions. Any of those mixing procedures which have been employed inthe art may be used. For example, all ingredients may be introduced intoa suitable power mixer together with water and mixed under heat to astate of homogeneity. The so-called quick-mix method is available. Herethe liquid bituminous binder and the mineral filler are first commingledin a mixer, after which the fibrous material and water are added andrapidly incorporated with a lowering of the temperature. The compositionis then preferably passed through one or more extrusion mixers of themasticator type. Yet again, the so-called dry-mix procedure may befollowed in which the binder in powdered condition is mixed with thefiber, the filler, and appropriate quantities of the resin (liquid) andwater to give an initial mix which is dry in the sense that it is aloose or powdery mass in spite of the presence of the liquids. Thismass, which then may be further homogenized as by treatment in aSprout-Waldron blender, is finally passed through one or more extrusionmasticators, wherein it is both homogenized and plasticized. It is usualto add water to the composition in the masticators to keep thetemperature down. I have noted that formulations utilizing exploded woodfibers generate more ,heat in the masticators so that it may beadvisable to add more water to control the temperature. Otherwise, nodifierences in processing or in molding are apparent. Compositionsutilizing exploded wood fibers mold well and make molded articles havingsmooth and attractive surfaces.

A study was made of various exploded wood fibers and various fiberlengths of the same fiber to determine whether the generalizations givenabove are correct. Exploded wood fibers were classified as to fiber sizein the following order: a +14 fraction, a +40 fraction, a +100 fraction,and a 1OO fraction. These size designations were determined using aClark screen classifier.

The following table will indicate approximately the percentagecomposition of the various fractions:

[Percent retained on screen] Fraction +8 +24 +50 80 I found that thefiber length had little or no effect on the impact resistance of themolded article. However, a microscopic study of the molded articlesrevealed that the larger fractions did not mix in as well. On the basisof this study, I have in my own work eliminated the use of the +14fraction, since it presents a danger of increasing apparent acidpenetration and absorption through the exposure at molded surfaces ofimproperly mixed or improperly incorporated fibrous masses. The orsmallest fraction does not increase the impact resistance ofcompositions proportionately as much as do the other fractions. Forexample, using equivalent quantities of the several fractions ofexploded cottonwood fibers, it was found that the 1OO fraction gave animpact resistance of 6.3. The largest fraction, namely the V creases inthe amount of resin present.

+14 fraction gave an impact resistancev of 7.6." The next largest or +40fraction gave a slightly lower impact resistance of 7.3; but the bestimpact resistance was given bythe +100 fraction of this fiber, namely animpact resistance of 7.8.

As a consequence of these considerations, I prefer to use exploded woodfibers of fiber lengths as given for the +40 and +100 fractions in thetable above.

As indicated above, exploded wood fibers from all wood sources, are'notidentical, although they have. in comon the general characteristics, setforth above. Of the. Commonly available exploded wood fibers, I prefercottonwood to the others which I rate. in the following order: alder,hemlock and Douglas fir. Weight for weight, the cottowood fiber appearsto produce greater impact resistances in all fractions thanthe other.wood fibers mentioned, which vary among themselves in effectiveness in.the several fractions. By way of example, the +100 fraction ofcottonwood in a given amount, gave an impact value of 7.8, whereas thesame fraction and amount of alder gave a value of 6.1, hemlock giving avalue of 5.0 and Douglas fir a value of 5.2.

The impact value of a cotton composition on the first formula givenabove, by the same test, was 5.7. When 11% of +100. cottonwood fiber wassubstituted for the 11% of cotton in an otherwise identicalcomposition,-the

impact resistance was only 4.6 by. the test, a value too.

low to be commercially significant. When, however, the

quantity of cottonwood fiber in the composition was in-.

creased in accordance with the teachings above, to a Value of 14.4%, theimpact value had risen to 6.7 by thesame test, which is definitely andmarkedly superiorto the im-. pact value of the comparable cottoncomposition. At this point, the acid absorption value of the explodedwood composition was less than half of that of the cotton composition,and had apparently attained a fixed value, whereas the acidabsorption-of the cotton com position was. still increasing at the endof 106 days of test.

Larger quantities. of. exploded wood will still furtherincrease impactresistance, resistance to bulging, tensile strength and the like whileretaining acid properties equal to or better than the acid properties ofcurrent cotton compositions, as has been set forth.

The resins which have been referred to hereinabove are those taughtinthe Dillehay Patent- 2,501,995, namely acid polymeri'zable resins chosenfrom a class consisting of partially polymerized furfuryl alcohol,phenol-furfural, phenol-formaldehyde, and mixtures thereof. That patentsuggested'the use of such resins in an amount substantially between 1/2% and 30% by weight'of the total binder, i. e. the asphalt or bitumenplus the resin. Economical considerations among other things willdetermine the amount of resin which will ordinarily be employed. While Ibelieve that the novel results which flow from the practice of myinvention are in large part dependent upon a coaction between explodedwood fibers and the combination of binder and resin, I desire to pointout that the use of exploded wood fibers enables me on the one hand tosecure an equal or superior acid resistance with a smaller quantity ofpolymerizable resin present, and on the other hand, to vary or modifythe specific acid absorption of exploded wood compositions containingany given amount of exploded wood fiber by increases or de- Thus it isreadily possible, economic conditions permitting, to maintain the sameultimate acid absorption with an increased, amount of wood fiber byincreasing the resin content of'the composition. This, of course, iswithin reasonable limits,

since the. resin, beingxa softer ingredient, tends to lower thestifiness and increase the penetration of any given bituminous binder,so that it is generally necessary tov compensate for'the softeningeffect .of' theresinby the employment of a harder binder as the resinquantityis increased.v Nevertheless as a generalrule, I prefer-to use anincrease in the amount of resin with an increase in the amount ofexploded wood as illustrated by'the following two exemplary formulae:

Wood Fiber ..percent. 14.0 11.0; Talc. V V V (10.-.- 34. 6 41: 0 Resin.-.do-..- 3.0 2.1 A sn'halt do 48. 4; p 45. 9

Test Cotton Exploded Linters Wood 2. 61 3. 0 7. 5 9. 0 1, 052 l, 240Flnn atinn 1. 44 I. 13 Tensile X Elongation 1, 548 1, 411 Bulge:

Side 0.031 0. 015 End 0. 119 0. 0 34 FORMULATION USED Asphalt. 46. 2 47.4 Talc. V 40. 0 35. 8 Fiber 11.0 14. O Resin 2. 8 2. 8

It will be noted that the exploded wood composition has a measurableadvantage in specific gravity. Its composition penetration is less. Itshows an advantage in both forms of the dropped ball impact test. Ithas. also a somewhat greater tensile strength. 'Its elongation valueissornewhat less, but it is comparable in'this value and in'the productof tensile'and elongation with the cotton linters composition. It'showsa distinctly lessened re sponse to both formsv of the standard bulgetest. Its acid absorption is markedly less, as indicated above. It willbe seen that the exploded wood container is a distinctly superiorproduct. The above figureswere taken from boxes produced in productionruns.

My invention contemplates the use ofexploded wood fibers in whole or inpart as the fibrous reinforcement in compositions and molded articles ofthe classes referred to. Exploded wood may be used as a partial orcomplete replacement for other types of fibers in such compositions andmoldedarticles. Further, a percentage ofexploded wood may be employed incompositions of this. class to increase impact resistances withoutsubstantially lowering acid values where the percentage of other fibersalso employed is. such as to give satisfactory acid'values. Thus, in astructure in which cotton is used, a part of the cotton may besubstituted by exploded wood fibres,

permitting the use of a somewhat greater total quantity of fibrousreinforcement without sacrifice of acid qualities, or the attainment. ofbetter acid qualitieswith equivalent physical properties. Similarlyarticles may be made with combinations. of papermakers fibre andexploded Wood fibre, as well as mixtures. of these with cotton or otherfibres.

Modifications may be made in my invention without departing from thespirit of it: Having thus described my invention in certain exemplaryembodiments, what l claim as new and desire to secure by Letters Patentis: I

1. An acid-resistant molding: composition comprising as a fibrousreinforcement substantially 13% to 25% of exploded Wood fiber andsubstantially 40% to 13% of non-fibrous, finely divided, acid-resistantfiller, the balance being a bituminous binder.

- 2. An acid-resistant molding composition comprising substantially 13%to 25% of exploded wood fiber and substantially 40% to 13% ofnon-fibrous, finely divided,

acid-resistant filler, the balance being a bituminous binder, includinga small quantity of an incompletely polymerized resin, acidpolymerizable to an acid-resistant state, and chosen from a classconsisting of partially polymerized furfuryl alcohol, phenol-furfural,phenol-formaldehyde and mixtures thereof.

3. The composition claimed in claim 1, wherein the quantity ofnon-fibrous filler varies inversely with the quantity of exploded woodfiber within the limits set forth.

4. The composition claimed in claim 2, wherein the quantity ofnon-fibrous filler varies inversely with the quantity of exploded woodfiber within the limits set forth, and in which the quantity of resin issubstantially 0.5% to varying directly with the quantity of explodedwood fiber within the limits set forth.

5. A molded storage battery container made from the molding compositionof claim 1.

6. A molded storage battery container made from the composition of claim2.

7. A molded storage battery container of good acid properties andsuperior physical characteristics comprising a bituminous binder, from13% to 25% by weight of exploded wood fiber and a non-fibrous,acid-resistant filler.

8. The article claimed in claim 7, comprising also as an ingredient from0.5% to 5% of an incompletely polymerized resin, acid polymerizable toan acid-resistant stage, and chosen from a class consisting of partiallypolymerized furfuryl alcohol, phenol-furfural, phenol-formaldehyde andmixtures thereof.

9. A bituminous molding composition containing a bituminous binder, afinely divided non-fibrous, acid-resistant filler, and exploded woodfiber as a fibrous reinforcement, the said exploded wood fiber beingsubstantially 13% to 25% by weight of the composition, and the saidfiber being of such size as to pass a -mesh screen and be retained on al00-mesh screen in the Clark classifier.

10. A molding composition consisting of substantially 14% exploded woodfiber, 33.6% talc, 48.4% bituminous binder and 3% of an incompletelypolymerized resin acid polymerizable to an acid-resistant state, andchosen from a class consisting of partially polymerized furfurylaleohol, phenol-furfural, phenol-formaldehyde and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,501,995 Dillehay Mar. 28, 1950 2,516,847 Boehm Aug. 1, 1950 2,601,597Daniel June 24, 1952

1. AN ACID-RESISTANT MOLDING COMPOSITION COMPRISING AS A FIBROUSREINFORCEMENT SUBSTANTIALLY 13% TO 25% OF EXPLODED WOOD FIBER ANDSUNSTANTIALLY 40% TO 13% OF NON-FIBROUS, FINELY DIVIDED, ACID-RESISTANTFILLER, THE BALANCE BEING A BITUMINOUS BINDER.